The present invention relates to a leadframe as a land grid array (LGA) in which multiple lands are arranged in columns and rows of external terminals exposed on the bottom of a package. This invention also relates to a resin-molded semiconductor device including the leadframe, a method of making the leadframe and a method for manufacturing the device.
In recent years, to catch up with rapidly advancing downsizing and performance enhancement of electronic units, it has become increasingly necessary to assemble semiconductor components at a higher and higher density. To meet this demand, a resin-molded semiconductor device, formed by molding a semiconductor chip and leads together with a resin encapsulant, has its size and thickness reduced noticeably. In parallel with this downsizing trend, the number of pins required for a single electronic unit is also increasing day after day.
Hereinafter, a known leadframe for use in a resin-molded semiconductor device will be described with reference to the drawings.
FIG. 12 illustrates a plan view of a known leadframe. The leadframe 100 shown in FIG. 12 is for use in a quad flat package (QFP) in which external pins extend outward from the four side faces of a rectangular parallelepiped package. As shown in FIG. 12, the leadframe 100 includes frame rail 101, rectangular die pad 102, inner leads 103 and outer leads 104. The die pad 102 is located at the center of the frame rail 101. The inner end of each inner lead 103 faces an associated side of the die pad 102 and the respective inner ends of the inner leads 103 are spaced apart from the sides of the die pad 102. The inner end of each outer lead 104 is connected to the outer end of the associated inner lead 103 while the outer end of each outer lead 104 is connected to the frame rail 101. The outer leads 104 are joined together by a tie bar 105 for preventing the overflow of a resin encapsulant during a resin molding process. And the die pad 102 is supported at the four corners by support pins 106 that are connected to the tie bar 105.
In FIG. 12, the members existing inside the dashed-line region 109 will be molded together by a resin encapsulant. Although just a part of the leadframe 100 for one device is illustrated in FIG. 12, the leadframe 100 actually has many other parts that each have the pattern shown in FIG. 12 and that are arranged in columns and rows.
FIG. 13 illustrates a cross-sectional structure for a resin-molded semiconductor device including the leadframe 100. In FIG. 13, each component also shown in FIG. 12 is identified by the same reference numeral.
As shown in FIG. 13, a semiconductor chip 107 is bonded onto the die pad 102 using some adhesive or solder. The semiconductor chip 107 is electrically connected to the inner leads 103 using metal fine wires 108. The die pad 102, semiconductor chip 107 on the die pad 102, metal fine wires 108 and inner leads 103 are molded together with a resin encapsulant 109A. In this case, the bottom of the die pad 102 is completely buried in the resin encapsulant 109A. The outer leads 104 extend outward from the side faces of the resin encapsulant 109A parallelly to the surface of the die pad 102 on which the chip 107 has been mounted. Also, the outer leads 104 have been bent downward so that this package can be surface-mounted onto a motherboard.
As described above, the number of components that should be integrated together within a single semiconductor chip 107, or the number of external electrodes (or pins) per chip, has been on the rise these days. Thus, the number of outer leads 104 should also be increased to catch up with this latest trend. That is to say, the number of inner leads 103, which are joined to the outer leads 104, should also be increased to cope with such an implementation. However, the width of the inner (or outer) leads 103 or 104 has a patternable limit. Accordingly, if the number of inner (or outer) leads 103 or 104 was further increased, the overall size of the leadframe 100 should also increase. This is not allowable because the increase in size of the leadframe 100 is incompatible with the recent downsizing trend. On the other hand, if the width of the inner or outer leads 103 or 104 were reduced, then it would be much more difficult to form the leadframe 100 in its desired shape.
To cope with these problems, face-bonded semiconductor devices, such as ball grid array (BGA) and land grid array (LGA) types, are also available recently. In semiconductor devices of these types, a semiconductor chip is mounted onto the non-circuitry side of a carrier (e.g., a printed wiring board), including ball or land electrodes on its back surface, and is electrically connected to these electrodes.
A semiconductor device of the BGA or LGA type is then mounted onto a motherboard so that its back surface faces the principal surface of the motherboard. And then the external electrodes (i.e., the ball or land electrodes), exposed on the back surface of the device, are directly connected electrically to the electrodes on the motherboard.
The BGA- or LGA-type semiconductor device, however, uses a multilayer carrier (or wiring board) in which ceramic or plastic layers have been stacked. Accordingly, the fabrication process thereof is overly complicated and the fabrication cost thereof is far from reasonable.
Also, it is hard to apply a method for manufacturing the known resin-molded semiconductor device shown in FIGS. 12 and 13 as it is to forming a semiconductor device of the BGA or LGA type. The reason is as follows. In the manufacturing process, part of a metal plate, including portions to be lands as external electrodes, should be connected to the frame rail with some joining/supporting members before the lands are formed. Accordingly, where lands should be arranged in three or more rows, the device of the BGA- or LGA-type device cannot be so small.
In addition, according to the method for manufacturing the known resin-molded semiconductor device shown in FIGS. 12 and 13, the device cannot be mounted onto the motherboard so accurately as in manufacturing a face-bonded semiconductor device of the BGA or LGA type. As described above, the beamlike outer leads 104 shown in FIG. 12 extend linearly outward from the sides of the resin encapsulant 109A just after the members of the device have been molded. Accordingly, the outer leads 104 should be bent downward so that the far end of each outer lead 104 has its bottom located at least no higher than the back surface of the resin encapsulant 109A. And in this bending process step, the outer leads 104 cannot be bent so uniformly and the far ends of the outer leads 104 are likely located at various levels.